Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenue	$ 142,642	$ 104,935	$ 222,536	$ 164,802
Cost of revenue	97,429	67,975	171,626	121,467
Gross profit	45,213	36,960	50,910	43,335
Operating expenses:
Technology and development	13,033	10,090	25,796	19,762
Marketing	14,435	10,132	27,770	20,591
General and administrative	15,288	12,466	32,062	26,833
Total operating expenses	42,756	32,688	85,628	67,186
Income (loss) from operations	2,457	4,272	(34,718)	(23,851)
Interest income and other income, net:
Interest income	729	32	1,307	76
Other income, net	21	0	179	13
Total interest income and other income, net	750	32	1,486	89
Net income (loss)	3,207	4,304	(33,232)	(23,762)
Accretion of redeemable convertible preferred stock	0	(110,921)	0	(135,690)
Net income (loss) attributable to common stock—basic	3,207	(106,617)	(33,232)	(159,452)
Net income (loss) attributable to common stock—diluted	$ 3,207	$ (106,617)	$ (33,232)	$ (159,452)
Net income (loss) attributable to common stock—basic (in dollars per share)	$ 0.04	$ (7.15)	$ (0.40)	$ (10.74)
Net income (loss) attributable to common stock—diluted (in dollars per share)	$ 0.04	$ (7.15)	$ (0.40)	$ (10.74)
Weighted average shares—basic (in shares)	83,164,670	14,913,234	82,590,979	14,840,759
Weighted average shares—diluted (in shares)	90,743,178	14,913,234	82,590,979	14,840,759